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Basics of Radiation Interactions in Matter
Published in Michael Ljungberg, Handbook of Nuclear Medicine and Molecular Imaging for Physicists, 2022
This means that -particles with higher energies than , but only these, are treated as new ionizing particles. is thus essentially the electronic stopping power but without the contribution from of secondary electrons with a kinetic energy higher than because these have such a high range that the energy cannot be considered locally absorbed. A typical value of can be 100 eV. Because LET is a measure of the density of ionizations along the particle track, it is a very important concept in radiobiology as the biological effect of radiation is largely dependent on the LET value.
Radiotherapy Physics
Published in Debbie Peet, Emma Chung, Practical Medical Physics, 2021
Andrea Wynn-Jones, Caroline Reddy, John Gittins, Philip Baker, Anna Mason, Greg Jolliffe
Radiobiology can inform radiotherapy practice at various levels. On a conceptual basis, modelling mechanisms and processes that explain observed responses of both tumour and normal tissues can be used to propose developments and adjustments to treatment strategies. Examples include either decreasing or increasing the number of treatment sessions (hypo- and hyper-fractionation schedules) or the use of agents to either sensitise cancer cells to radiation effects (cell sensitisers) or protect healthy tissue. A good example of hypo-fractionated radiotherapy is a treatment technique known as Stereotactic Ablative Body Radiotherapy (SABR) where high doses of precisely targeted radiation are used to control small tumours, typically in the lung or for cancer that has only just spread to other areas. In SABR, treatment is delivered over relatively few visits compared to conventional radiotherapy treatments.
Summary, Conclusions, and Implications
Published in T. D. Luckey, Radiation Hormesis, 2020
The general conclusion suggests a new goal for radiobiology: understand the biopositive effects of ionizing radiation. Radiation hormesis and the possible essentiality of ionizing radiation provide new concepts, new questions, and incentive for new directions in radiation research. Discussions, planning, energy, and resources must change from emphasis on excess exposure to consideration of chronic supplementation of background ionizing radiation. This concerns most people every day of their lives. The establishment of radiation hormesis as the best model for dose-response effects of ionizing radiation, plus the acceptance of ionizing radiation as an essential agent, have tremendous implications for all people.
BIGART 2019 – adapting to the future
Published in Acta Oncologica, 2019
Jens Overgaard, Ludvig Paul Muren, Morten Høyer, Cai Grau
While the technical abilities for advanced treatment delivery currently dominates the field of radiation oncology, the importance of utilizing and understanding clinical radiobiology gradually returns to the focus area. This takes place partly through well designed studies where predictive parameters are being applied in order to select the right patients for the right treatment [76–82]. This happens through analyses of risk factors associated with treatment related morbidity, such as cardiovascular problems or risk of radiation induced secondary cancer, and also by focusing on variation in tumor radiosensitivity, such as the influence of human papillomavirus (HPV) positivity related to the irradiation treatment of squamous cell carcinomas [83,84]. The need to link such variation in radiosensitivity with a given radiation treatment, demands a very clear understanding of the irradiated volumes and site of treatment failure [85–88]. Again, such information will have to come from carefully designed prospective studies and the tradition of having large clinical databases in the Nordic countries, is an obvious advantage for this type of analysis. The importance of clinical radiobiology is also gaining renewed interest, not only by the endless discussion of the role of hypoxia and its imaging [37–40,89–91], but even more in the attempt to escalate or de-escalate the tumor dose. In this aspect optimal fractionation is of outmost importance, and (accelerated) hyperfractionation is gaining a renewed justified role to optimize dose escalation [73,84].
Radiation-induced bystander phenomenon: insight and implications in radiotherapy
Published in International Journal of Radiation Biology, 2019
Sharmi Mukherjee, Anindita Chakraborty
Bystander cells have the ability to generate intercellular feedback signals which can rescue the irradiated cells from deleterious effects of ionizing radiations. This phenomenon is known as Rescue Effect (Figure 4). The benefits derived by irradiated cells include significant reduction of ROS generation with decrease in number of DNA double-strand breaks, thereby promoting cellular survival and genomic stability. The signaling molecules involved in such rescue effect include growth factors like cytokines, cAMP which can promote angiogenesis, repopulation, and re-myelination of ionizing radiation-damaged cells (Dilmanian et al. 2007, Chen et al. 2011, Widel et al. 2012, Lam et al. 2015). Reports suggest that bystander fibroblasts, both normal and cancer associated, have a contributory role in eliciting rescue effects in targeted cells and the intensity of such effects is regulated by the number of the adjacent unirradiated cells (Choi et al. 2012a, Chu et al. 2014). It has been observed experimentally that even when the bystander cells have insufficient cAMP, they still supply cAMP to the irradiated cells to protect them from radiation damages (He et al. 2014, Lam et al. 2015). However, the precise mechanism which triggers such behavior of bystander cells is yet to be understood. In clinical radiobiology, such rescue of radiation-targeted cancer cells is undesirable and can prove to be highly disadvantageous in terms of radiotherapeutic efficacy. Thus, in planning of radiotherapy dose protocols, studies of not only the bystander effects but also the rescue effects, if any, on the targeted cells need to be considered.
The paradox of adaptive responses and iso-effect per fraction
Published in International Journal of Radiation Biology, 2018
While the iso-effect per fraction assumption would preclude the observation of adaptive responses for cells survival after radiotherapy fractions, this does not preclude the observation of adaptive responses for other endpoints. Adaptive responses for cell survival might also manifest without invalidating the iso-effect principle in practical terms. It may also be the case that instances of both phenomena can be observed under different conditions, but not at the same time. The ongoing clinical research into dose, duration and fractionation schedules suggests that while our models assist us to make predictions, the radiobiology that underpins tissue and tumour responses to sequential irradiations is not yet ready to give up all its secrets. But, the iterative and progressive nature of science means that sometimes new ideas may replace old ones, that things that seemed simple may be more complicated that they appeared, and every so often, that both sides of the argument turn out to be correct.